1. Field of the Invention
The present invention relates to an optical transmission system for transmitting signal light (multiplexed signal light), where a plurality of signal channels included in a signal wavelength band are multiplexed, via an optical fiber transmission line.
2. Related Background Art
A Wavelength Division Multiplexing (WDM) optical transmission system transmits multiplexed signal light including a plurality of signal channels via an optical fiber transmission line so as to enable the high-speed transmission/reception of large capacity information. The optical transmission system can suppress waveform deterioration of signal light by decreasing the absolute value of the accumulated chromatic dispersion of an entire signal light propagation path. By this, the optical transmission system can increase the bit rate and allow larger capacity.
For example, the optical transmission system disclosed in Japanese Patent Laid-Open No. 11-204866 has a configuration for demultiplexing a plurality of signal channels included in the multiplexed signal light into a plurality of bands, and performing dispersion compensation for each band, by this, the absolute value of the accumulated chromatic dispersion is decreased for each band.
In Document 1, “D. A. Atlas, ‘Chromatic dispersion limitations due to semiconductor laser chirping in conventional and dispersion-shifted single-mode fiber systems’, Optics Letters, Vol. 13, No. 11, pp. 1035-1037 (1988)”, the relationship between the accumulated chromatic dispersion and the transmission characteristics, in a system where a direct modulation semiconductor laser light source is applied for the signal light source, is shown. In Document 1, the values of dispersion resistance, to acquire good signal light transmission quality, are stated, where the dispersion resistance is 1200 ps/nm when the bit rate is 2.5 Gb/s, and the dispersion resistance is 80 ps/nm when the bit rate is 10 Gb/s.
The optical transmission system stated in Document 2, “M. Kakui, et al, ‘2.4 Gbit/s repeaterless transmission over 306 km non-dispersion-shifted fiber using directly modulated DFB-LD and dispersion-compensating fiber’, Electronics Letters, Vol. 31, No. 1, pp. 51-52, (1995)” intends to make the absolute value of accumulated chromatic dispersion to roughly zero, where the direct modulation semiconductor laser light source is used as the signal light source and dispersion-compensating optical fiber is used as the dispersion compensator.
Also in the optical transmission system stated in Document 3, “M. Tanaka, et al, ‘Water-peak-suppressed non-zero dispersion shifted fiber for full spectrum coarse WDM transmission in metro networks’, OFC 2002, WA2”, an optical fiber having a loss peak due to an OH-radical near the wavelength of 1.38 μm is decreased, is applied. Document 3 shows the case where a direct modulation semiconductor laser light source is used for the signal light source, where the accumulated chromatic dispersion is about 1000 ps/nm and the transmission penalty is 1 dB when the bit rate is 2.5 Gb/s.